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.Dd September 12, 2019
.Dt MAT_VARCREATESTRUCT 3
.Os
.Sh NAME
.Nm Mat_VarCreateStruct
.Nd Creates a structure variable.
.Sh SYNOPSIS
.Fd #include <matio.h>
.Ft matvar_t *
.Fo Mat_VarCreateStruct
.Fa "const char *name"
.Fa "int rank"
.Fa "size_t *dims"
.Fa "const char **fields"
.Fa "unsigned nfields"
.Fc
.Sh DESCRIPTION
The
.Fn Mat_VarCreateStruct
function creates a structure variable named
.Fa name
that can be written to a MAT file.
.Sh RETURN VALUES
If the structure variable was successfully created, a pointer to the variable
is returned.
Otherwise NULL is returned.
The structure variable pointer should be free'd when no longer needed using
.Fn Mat_VarFree .
The names of the fields are copied in the function, and thus should be released
after calling the function if necessary.
.Sh EXAMPLES
This example program opens a MAT file named by the first argument to the
program, and writes a structure named
.Em a
to the file.
.Bd -literal
#include "matio.h"

int
main(int argc, char **argv)
{
    mat_t    *matfp;
    matvar_t *matvar;
    matvar_t *field;
    const char *fields[2] = {"field1", "field2"};
    double       data1 = 1, data2 = 2;
    size_t       dims[2] = {1, 1};

    matfp = Mat_Open(argv[1], MAT_ACC_RDWR);
    if ( NULL == matfp ) {
        fprintf(stderr, "Error opening MAT file %s\n", argv[1]);
        return EXIT_FAILURE;
    }

    dims[0] = 1; dims[1] = 1;
    matvar = Mat_VarCreateStruct("a", 2, dims, fields, 2);
    if ( NULL == matvar ) {
        Mat_Close(matfp);
        return EXIT_FAILURE;
    }

    field = Mat_VarCreate(NULL, MAT_C_DOUBLE, MAT_T_DOUBLE, 2, dims, &data1,
                MAT_F_DONT_COPY_DATA);
    Mat_VarSetStructFieldByName(matvar, "field1", 0, field);

    field = Mat_VarCreate(NULL, MAT_C_DOUBLE, MAT_T_DOUBLE, 2, dims, &data2,
                MAT_F_DONT_COPY_DATA);
    Mat_VarSetStructFieldByName(matvar, "field2", 0, field);

    Mat_VarWrite(matfp, matvar, MAT_COMPRESSION_NONE);
    Mat_VarFree(matvar);

    Mat_Close(matfp);
    return EXIT_SUCCESS;
}
.Ed
.Sh SEE ALSO
.Xr Mat_VarCreate 3 ,
.Xr Mat_VarSetStructFieldByName 3
